This invention relates generally to carbureting devices for gas turbine engines and, more particularly, to gas turbine engine systems having low pressure fuel injectors commonly referred to as fuel cups.
Gas turbine engines generally comprise a compressor for pressurizing air and a combustor for burning the fuel with a portion of the pressurized air and heating the remaining pressurized air or a large portion thereof which is then flowed into a turbine to generate power. Fuel that is burned is normally premixed with air prior to undergoing combustion in order to minimize smoke and other undesirable by-products and maximize the efficiency of the combustion process. The carbureting device is designed to atomize the fuel, and premix it with air in order to effect efficient and complete combustion. A very common problem is coking, a phenomenon which is a build up of carbon caused by unburnt fuel being heated at nonstoichiometric conditions on hot surfaces. This deposition of carbon leads to a build up or coking which clogs passageways and seriously degrades the engine's operation.
Spray atomizing nozzles have been used in the past with varying degrees of success for the prevention of coking which in turn blocks nozzle passages and leads to inefficient combustion and expensive repairs. Efficient spray atomizers may also require high pressure systems which add weight and cost to fuel supply systems, a consequence which gas turbine engine designers are constantly seeking to avoid.
Low pressure fuel systems have been designed which incorporate primary and secondary counterrotational air swirlers which atomize fuel by the high shear forces developed in the area or zone of interaction between the two counterrotational flows. Such designs require thin fuel injectors that are prone to coking or require complicated and expensive air systems to prevent coking. Yet other suggested low pressure fuel injectors mix air and fuel upstream of the air swirlers, such as in U.S. Pat. Nos. 3,667,221 and 3,811,278, before injecting the air and fuel mixture into a spin chamber. These schemes also experience coking in the areas containing the swirling vanes and on the vanes as well.